(1) Field of the Invention
The present invention pertains to a rabbet joint between two component parts and a method of forming a rabbet joint. More particularly, the present invention pertains to an apparatus and method for eliminating the radius commonly formed between the faces of an annular rabbet.
(2) Description of the Related Art
When joining components of an assembly, a rabbet is often useful on at least one of the components to provide a plurality of engagement surfaces between mating components of the assembly. In addition to providing structural support, rabbets also facilitate proper alignment of the components with respect to each other.
Typically, a rabbet takes the form of a right-angle groove or channel made into the edge of a component part that is adapted to receive and engage the corner of a mating component. As an example, rabbets are used to facilitate the assembly of components in dynamoelectric devices. Dynamoelectric devices are commonly comprised of, a rotor and shaft assembly, a stator encircling the rotor and shaft assembly, a cylindrical shell housing secured to and encircling the stator, and a pair of end shields secured to the ends of the housing. Because the end shields typically support bearings mounted on the rotor and shaft assembly and thereby position the rotor and shaft assembly relative to the stator, proper alignment of the end shields with respect to the housing can be critical to the operation of the dynamoelectric device. It is therefore common to provide a rabbet around the edge of the end shield to ensure that proper alignment with the housing is made.
A prior art end shield is shown in FIG. 1. The end shield 10 has a hole 12 that allows a shaft of a dynamoelectric device to pass therethrough. An annular boss 14 extends around the hole 12 and is adapted to support a bearing mounted on the shaft. The end shield 10 also has a cylindrical rim 16 protruding from the perimeter of its main body and has a rabbet 18 formed thereon. Although end shields similar to the end shield 10 shown are common in the industry, many variations exist. For example, in FIG. 1 the end shield 10 is shown having a solid web 19 extending from the boss 14 to the rim 16. However, it is also common to have a plurality of spokes extending radially from the boss 14 to the rim 16 with ventilation openings therebetween in place of the solid web 19. Similarly, it is not necessary for an end shield to have a hole 12 for passage of the shaft therethrough, nor that the rim 16 extend axially from the main body. It is an improvement to the prior art annular rabbet 18 that is a focus of this invention.
The particular prior art rabbet 18 is formed on the rim 16 of the end shield 10. The rabbet 18 is comprised of a cylindrical surface 20 and an adjacent, perpendicular annular surface 22. The two surfaces form a right-angle shoulder around the rim 16 adapted to engage an end of a cylindrical shell housing of the dynamoelectric device. The diameter of the cylindrical surface 20 is approximately equal to that of a cylindrical interior surface of the housing nearest the housing end. Thus when the end shield 10 is assembled onto the housing, the cylindrical surface 20 engages the interior surface, thereby radially positioning and supporting the end shield 10 relative to the housing. Similarly, the annular surface 22 is designed to axially position the end shield 10 relative to the housing by engaging an annular end surface of the housing that is perpendicular to the interior surface of the housing. Once in proper alignment, the components may be further secured to each other by fasteners, adhesives, interlocking tabs or catches, or by other means for securing together components of an assembly as known to those skilled in the art.
As shown in the detailed cross-section of the prior art rabbet 18 in FIG. 2, a radius 24 is often inadvertently formed between the annular surface 22 and the cylindrical surface 20. This radius 24 can be the result of cutting tool wear when a machining process is used to form the rabbet 18 on the end shield 10. Additionally, the radius 24 may be the result of wear of the dies or molds used to cast or mold the end shields 10. When precise alignment of the components within an assembly is required, any radius 24 formed between the annular surface 22 and the cylindrical surface 20 is undesirable in that, the radius 24 may prevent the annular surface 22 from engaging its mating component resulting in improper axial alignment of the components and the undesirable appearance of a gap between the end shield 10 and the shell housing.
Prior art solutions to this problem include reworking the end shield 10 by machining the rabbet 18 using sharp cutting tools to reduce the radius 24. The extra machining process required by this solution greatly adds to the expense of production. Since the preferred method of fabrication is to mold or cast the end shields 10, another solution has been to periodically rework or replace the molds or dies. This solution unnecessarily burdens the production process when the molds and dies are otherwise adequate. Yet another solution is to provide a chamfer or radius on the housing between the interior surface and the annular end surface of the housing that is larger than that of the radius 24, thus providing relief in the housing for the radius 24 when the components are properly aligned. Like the other solutions, modifying the housing increases the cost of production and it is therefore desirable to find alternative solutions to the problem that can eliminate the radius 24 without adding a process step or otherwise increasing the cost of production.
The present invention overcomes the problems associated with prior art rabbet joints by utilizing a plurality of separated coplanar surfaces in place of the prior art annular surface 22 and by positioning a plurality of cylindrical surface segments perpendicular to and between the coplanar surfaces. The aggregate of the cylindrical surface segments replaces the cylindrical surface 20 of the prior art rabbet 18. In accordance with this invention, no common edge is formed between the coplanar surfaces and adjacent cylindrical surface segments and, therefore, no radius 24 can be formed regardless of die, mold, or tool wear during the manufacturing process. This invention allows a component, such as an end shield, to be molded or cast with an annular rabbet type fitting and to align perfectly when assembled to a sharp edged mating component, regardless of minor die or mold wear.